The invention relates to traction roller transmissions in which motion is transmitted from an input shaft to an output shaft by traction rollers arranged between, and in engagement with, toric discs mounted opposite each other on the input and output shafts.
In such transmissions, the traction rollers are supported on support trunnions which permit pivoting of the traction rollers for adjustment of different transmission ratios. A change of the transmission ratio is initiated by slight axial movement of the trunnions in either axial direction out of their center positions, which movement causes the traction rollers to climb to different circles of engagement with the toric discs. When a new desired transmission ratio is reached, the trunnions return to their axial center positions while the trunnions with the traction rollers remain pivoted in their new transmission ratio position. Axial movement of the trunnions is suitably obtained by hydraulic means such as cylinder and piston structures which are arranged axially adjacent the trunnions to apply axial precess forces thereby by controlling admission of pressurized fluid to the cylinder and piston structures. In order to facilitate proper ratio adjustment, the trunnions are preferably provided with cam structures which cause the cam followers to have a predetermined position for each pivot position of the associated trunnions. Such cam structures however are relatively bulky and relatively expensive to manufacture.